The present invention refers to a master petal for the divergent zone of a convergent-divergent nozzle of variable geometry capable of orienting the flow of gas for a gas turbine engine, used as means of propulsion in aviation.
More specifically, in a preferred application, the nozzle to which the present invention relates is of the axisymmetric type comprising a convergent zone followed, in the direction of flow, by a divergent zone, both of which are formed by master petals connected to each other by articulations and slave petals, also connected together by articulations. The convergent zone, which is also of variable geometry, may be actuated so as to direct the flow of gas and therefore the thrust in any direction on a cone directed around the longitudinal axis of the engine.
Maneuverability of airplanes is essential. Maneuverability has been obtained up to now by aerodynamic forces, but it can be substantially improved by changing the orientation of the flow from its normal axial direction of actuation.
Orienting the flow of gas has been used for many years in rocket engines. In those engines, the systems are much simpler, since their nozzles are of constant geometry.
Convergent-divergent nozzles of variable geometry have relatively recently been introduced in supersonic airplanes driven by turbojet or turboprop engines. In this class of nozzles, systems for orienting the flow are still not in an operating phase. Those of the two-dimensional type in which the flow is directed only in one plane are in a more advanced state.
It is of particular advantage to orient the flow in nozzles with axial symmetry since the direction of the flow can then be varied in any axial plane, with the pitch and yaw planes being particularly important.
Various prior patents cover mechanisms for orienting the flow in this type of nozzle, since it is theoretically possible to effect it in various ways, although it is very difficult for the mechanisms not to have a high degree of complexity.
To orient only the divergent zone of the nozzle downstream of the A8 throat area has the advantage that the disturbances induced by the orientation are not transmitted upstream of the engine and that the sealing of the spaces between the different moving parts is simplified. There still remains the problem of the seal between divergent master petals during the orienting of the flow. With regard to this, reference should be had to U.S. patent application Ser. No. 336,369 of 1989 U.S. Pat. No. 4,994,660 and to Spanish Application No. 9200369 of 1992, which disclose different embodiments of nozzles in which only the divergent zone or a part of it respectively is oriented.
In order to seal the spaces between divergent master petals, various solutions are suggested in U.S. patent application Ser. Nos. 804,021 of 1985 now abandoned, 804,022 of 1985 now abandoned, 336,380 of 1989 now abandoned, and 07/475,465 of 1991 now U. S. Pat Ser. No. 5076996, and Spanish Applications Nos. 9,200,369 and 9,202,157 of 1992.
Spanish Patent Application 9,202,157 describes a concept of a divergent slave petal for sealing the longitudinal space between contiguous divergent master petals. The geometry of the longitudinal spaces between divergent master petals is changed during the orientation of the flow, changing from an approximately rectangular shape to that of an adjusted surface, the sides of which are no longer parallel.
Spanish Patent Application No. 9200369 of 1992 describes an orientable axisymmetric nozzle of variable geometry for gas turbine engines. That nozzle includes a convergent zone and a divergent zone, which are both formed of master petals and slave petals, and it includes control and outer radial support means for regulating the throat area and control means for regulating the orientation of the flow. Its novel feature is the fact that the variation of the A8 throat area and the orientation of the flow are effected by a single control system which is formed of three annular parts which are concentric to each other and to the axis of the engine, and of a plurality of linear actuators articulated at their upstream end to the structure of the engine.
The annular parts are connected to each other and to the structure of the engine by articulation elements and guide devices. Those permit the joint axial displacement of the three annular parts by the same amount with respect to the structure of the engine, and permit movement of relative rotation of the intermediate and outer annular parts with respect to each other and with respect to the inner annular part. This permits the inclination of the external annular part in any direction, with the center of rotation on the axis of the engine.
The convergent master petals are connected at their upstream ends to the inner annular part by tangential cylindrical articulations, the axes of which are perpendicular to the axis of the engine. The outer annular part, in turn, is connected by spherical articulations to the downstream end of the linear actuators.
The mechanism for variation of the A8 throat area is formed of a connecting rod which is connected at one end by an articulation to the convergent master petal, while at the opposite end it is connected by another articulation to the fixed structure of the cover of the nozzle.
The master petals of the divergent zone are subdivided transversely into two sections which are connected together by a cylindrical articulation, having an axis which is perpendicular to the axis of articulation between master petals of the convergent and divergent zones. The downstream section is connected to the outer annular part by a bar which is connected to that section by a spherical articulation and to the outer annular part by a tangential cylindrical articulation and the axis of the latter articulation is perpendicular to that of the engine.
The upstream section of the divergent master petal is connected, at its upstream end, to the corresponding convergent master petal by a tangential cylindrical articulation which has an axis that is perpendicular to the axis of the engine.
The outer annular part is formed of two ring segments which are interconnected with articulations and are supported by four linear actuators. This embodiment formed of two half rings moved by four linear actuators makes it possible to vary the A9 exit area for a fixed value of the A8 throat area.
Spanish Patent Application No. 9202157 of 1992 proposes converting every divergent slave petal into a deformable structural unit of minimum stiffness in torsion, formed of a base plate and a plurality of discrete transverse elements inserted in the base plate. The base plate imparts axial stiffness to the unit, serving as element for bearing the axial forces due to the flow of gas, the cooling air and the inertia forces, but presenting minimum capacity for transmitting transverse forces. On their part, the discrete transverse elements lack an ability to transmit torsion, but they do transmit the transverse forces and the shearing forces imposed both by the flow of gas and by the divergent master petals to which the gas pressure exerted on the base plate bearing the axial forces is transmitted.
Thus, Spanish Patent Applications 9200369 and 9202157 of 1992 disclose a mechanism capable of orienting the flow of gas by acting solely on a part of the divergent zone of the nozzle with suitable sealing of the longitudinal space between contiguous divergent master petals. The present invention describes and claims a divergent master petal which makes it possible to increase the maximum angle of orientation of the flow over that which is obtainable with the embodiment in Spanish Patent Application No. 9200369.
In orienting the divergent zone of the nozzle, the divergent master petals, as described in Spanish Patent Application No. 9200369, are forced to move in radial and tangential directions with respect to the central axis of the engine. The maximum angle of orientation of the divergent zone for a given A8 throat area is limited by the interferences between master and slave petals in zones near the outlet area A9. As indicated previously, Spanish Patent Application 9202157 of 1992 proposes converting the divergent slave petal into a deformable structural unit of minimum stiffness in torsion, formed by a base plate bearing the axial forces and with minimum capacity to transmit transverse forces. The base plate includes discrete transverse elements with capacity to transmit the transverse forces and the shearing forces imposed both by the flow of gas and by the divergent master petals. If the inner surface, in contact with the flow of gas, of the divergent master petals is flat, the maximum angle of orientation of the flow is determined by interference in zones close to the A9 exit area of the inner surface with the discrete transverse elements because in this case, the longitudinal edges of the base plate do not rest on the inner surface of the divergent master petals, a longitudinal opening appearing which permits the passage of the gases to the outside.